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+++ b/man/xemacs/mule.texi	Mon Aug 13 11:28:15 2007 +0200
@@ -0,0 +1,540 @@
+@c This is part of the Emacs manual.
+@c Copyright (C) 1997 Free Software Foundation, Inc.
+@c See file emacs.texi for copying conditions.
+@node Mule, Major Modes, Windows, Top
+@chapter World Scripts Support
+@cindex MULE
+@cindex international scripts
+@cindex multibyte characters
+@cindex encoding of characters
+
+@cindex Chinese
+@cindex Greek
+@cindex IPA
+@cindex Japanese
+@cindex Korean
+@cindex Russian
+  If you compile XEmacs with mule option, it supports a wide variety of
+world scripts, including Latin script, as well as Arabic script,
+Simplified Chinese script (for mainland of China), Traditional Chinese
+script (for Taiwan and Hong-Kong), Greek script, Hebrew script, IPA
+symbols, Japanese scripts (Hiragana, Katakana and Kanji), Korean scripts
+(Hangul and Hanja) and Cyrillic script (for Beylorussian, Bulgarian,
+Russian, Serbian and Ukrainian).  These features have been merged from
+the modified version of Emacs known as MULE (for ``MULti-lingual
+Enhancement to GNU Emacs'').
+
+@menu
+* Mule Intro::              Basic concepts of Mule.
+* Language Environments::   Setting things up for the language you use.
+* Input Methods::           Entering text characters not on your keyboard.
+* Select Input Method::     Specifying your choice of input methods.
+* Coding Systems::          Character set conversion when you read and
+                              write files, and so on.
+* Recognize Coding::        How XEmacs figures out which conversion to use.
+* Specify Coding::          Various ways to choose which conversion to use.
+@end menu
+
+@node Mule Intro, Language Environments, Mule, Mule
+@section Introduction to world scripts
+
+  The users of these scripts have established many more-or-less standard
+coding systems for storing files.
+@c XEmacs internally uses a single multibyte character encoding, so that it
+@c can intermix characters from all these scripts in a single buffer or
+@c string.  This encoding represents each non-ASCII character as a sequence
+@c of bytes in the range 0200 through 0377.
+XEmacs translates between the internal character encoding and various
+other coding systems when reading and writing files, when exchanging
+data with subprocesses, and (in some cases) in the @kbd{C-q} command
+(see below).
+
+@kindex C-h h
+@findex view-hello-file
+  The command @kbd{C-h h} (@code{view-hello-file}) displays the file
+@file{etc/HELLO}, which shows how to say ``hello'' in many languages.
+This illustrates various scripts.
+
+  Keyboards, even in the countries where these character sets are used,
+generally don't have keys for all the characters in them.  So XEmacs
+supports various @dfn{input methods}, typically one for each script or
+language, to make it convenient to type them.
+
+@kindex C-x RET
+  The prefix key @kbd{C-x @key{RET}} is used for commands that pertain
+to world scripts, coding systems, and input methods.
+
+
+@node Language Environments, Input Methods, Mule Intro, Mule
+@section Language Environments
+@cindex language environments
+
+  All supported character sets are supported in XEmacs buffers if it is
+compile with mule; there is no need to select a particular language in
+order to display its characters in an XEmacs buffer.  However, it is
+important to select a @dfn{language environment} in order to set various
+defaults.  The language environment really represents a choice of
+preferred script (more or less) rather that a choice of language.
+
+  The language environment controls which coding systems to recognize
+when reading text (@pxref{Recognize Coding}).  This applies to files,
+incoming mail, netnews, and any other text you read into XEmacs.  It may
+also specify the default coding system to use when you create a file.
+Each language environment also specifies a default input method.
+
+@findex set-language-environment
+  The command to select a language environment is @kbd{M-x
+set-language-environment}.  It makes no difference which buffer is
+current when you use this command, because the effects apply globally to
+the XEmacs session.  The supported language environments include:
+
+@quotation
+Chinese-BIG5, Chinese-CNS, Chinese-GB, Cyrillic-ISO, English, Ethiopic,
+Greek, Japanese, Korean, Latin-1, Latin-2, Latin-3, Latin-4, Latin-5.
+@end quotation
+
+  Some operating systems let you specify the language you are using by
+setting locale environment variables.  XEmacs handles one common special
+case of this: if your locale name for character types contains the
+string @samp{8859-@var{n}}, XEmacs automatically selects the
+corresponding language environment.
+
+@kindex C-h L
+@findex describe-language-environment
+  To display information about the effects of a certain language
+environment @var{lang-env}, use the command @kbd{C-h L @var{lang-env}
+@key{RET}} (@code{describe-language-environment}).  This tells you which
+languages this language environment is useful for, and lists the
+character sets, coding systems, and input methods that go with it.  It
+also shows some sample text to illustrate scripts used in this language
+environment.  By default, this command describes the chosen language
+environment.
+
+@node Input Methods, Select Input Method, Language Environments, Mule
+@section Input Methods
+
+@cindex input methods
+  An @dfn{input method} is a kind of character conversion designed
+specifically for interactive input.  In XEmacs, typically each language
+has its own input method; sometimes several languages which use the same
+characters can share one input method.  A few languages support several
+input methods.
+
+  The simplest kind of input method works by mapping ASCII letters into
+another alphabet.  This is how the Greek and Russian input methods work.
+
+  A more powerful technique is composition: converting sequences of
+characters into one letter.  Many European input methods use composition
+to produce a single non-ASCII letter from a sequence that consists of a
+letter followed by accent characters.  For example, some methods convert
+the sequence @kbd{'a} into a single accented letter.
+
+  The input methods for syllabic scripts typically use mapping followed
+by composition.  The input methods for Thai and Korean work this way.
+First, letters are mapped into symbols for particular sounds or tone
+marks; then, sequences of these which make up a whole syllable are
+mapped into one syllable sign.
+
+  Chinese and Japanese require more complex methods.  In Chinese input
+methods, first you enter the phonetic spelling of a Chinese word (in
+input method @code{chinese-py}, among others), or a sequence of portions
+of the character (input methods @code{chinese-4corner} and
+@code{chinese-sw}, and others).  Since one phonetic spelling typically
+corresponds to many different Chinese characters, you must select one of
+the alternatives using special XEmacs commands.  Keys such as @kbd{C-f},
+@kbd{C-b}, @kbd{C-n}, @kbd{C-p}, and digits have special definitions in
+this situation, used for selecting among the alternatives.  @key{TAB}
+displays a buffer showing all the possibilities.
+
+   In Japanese input methods, first you input a whole word using
+phonetic spelling; then, after the word is in the buffer, XEmacs
+converts it into one or more characters using a large dictionary.  One
+phonetic spelling corresponds to many differently written Japanese
+words, so you must select one of them; use @kbd{C-n} and @kbd{C-p} to
+cycle through the alternatives.
+
+  Sometimes it is useful to cut off input method processing so that the
+characters you have just entered will not combine with subsequent
+characters.  For example, in input method @code{latin-1-postfix}, the
+sequence @kbd{e '} combines to form an @samp{e} with an accent.  What if
+you want to enter them as separate characters?
+
+  One way is to type the accent twice; that is a special feature for
+entering the separate letter and accent.  For example, @kbd{e ' '} gives
+you the two characters @samp{e'}.  Another way is to type another letter
+after the @kbd{e}---something that won't combine with that---and
+immediately delete it.  For example, you could type @kbd{e e @key{DEL}
+'} to get separate @samp{e} and @samp{'}.
+
+  Another method, more general but not quite as easy to type, is to use
+@kbd{C-\ C-\} between two characters to stop them from combining.  This
+is the command @kbd{C-\} (@code{toggle-input-method}) used twice.
+@ifinfo
+@xref{Select Input Method}.
+@end ifinfo
+
+  @kbd{C-\ C-\} is especially useful inside an incremental search,
+because stops waiting for more characters to combine, and starts
+searching for what you have already entered.
+
+@vindex input-method-verbose-flag
+@vindex input-method-highlight-flag
+  The variables @code{input-method-highlight-flag} and
+@code{input-method-verbose-flag} control how input methods explain what
+is happening.  If @code{input-method-highlight-flag} is non-@code{nil},
+the partial sequence is highlighted in the buffer.  If
+@code{input-method-verbose-flag} is non-@code{nil}, the list of possible
+characters to type next is displayed in the echo area (but not when you
+are in the minibuffer).
+
+@node Select Input Method, Coding Systems, Input Methods, Mule
+@section Selecting an Input Method
+
+@table @kbd
+@item C-\
+Enable or disable use of the selected input method.
+
+@item C-x @key{RET} C-\ @var{method} @key{RET}
+Select a new input method for the current buffer.
+
+@item C-h I @var{method} @key{RET}
+@itemx C-h C-\ @var{method} @key{RET}
+@findex describe-input-method
+@kindex C-h I
+@kindex C-h C-\
+Describe the input method @var{method} (@code{describe-input-method}).
+By default, it describes the current input method (if any).
+
+@item M-x list-input-methods
+Display a list of all the supported input methods.
+@end table
+
+@findex select-input-method
+@vindex current-input-method
+@kindex C-x RET C-\
+  To choose an input method for the current buffer, use @kbd{C-x
+@key{RET} C-\} (@code{select-input-method}).  This command reads the
+input method name with the minibuffer; the name normally starts with the
+language environment that it is meant to be used with.  The variable
+@code{current-input-method} records which input method is selected.
+  
+@findex toggle-input-method
+@kindex C-\
+  Input methods use various sequences of ASCII characters to stand for
+non-ASCII characters.  Sometimes it is useful to turn off the input
+method temporarily.  To do this, type @kbd{C-\}
+(@code{toggle-input-method}).  To reenable the input method, type
+@kbd{C-\} again.
+
+  If you type @kbd{C-\} and you have not yet selected an input method,
+it prompts for you to specify one.  This has the same effect as using
+@kbd{C-x @key{RET} C-\} to specify an input method.
+
+@vindex default-input-method
+  Selecting a language environment specifies a default input method for
+use in various buffers.  When you have a default input method, you can
+select it in the current buffer by typing @kbd{C-\}.  The variable
+@code{default-input-method} specifies the default input method
+(@code{nil} means there is none).
+
+@findex quail-set-keyboard-layout
+  Some input methods for alphabetic scripts work by (in effect)
+remapping the keyboard to emulate various keyboard layouts commonly used
+for those scripts.  How to do this remapping properly depends on your
+actual keyboard layout.  To specify which layout your keyboard has, use
+the command @kbd{M-x quail-set-keyboard-layout}.
+
+@findex list-input-methods
+  To display a list of all the supported input methods, type @kbd{M-x
+list-input-methods}.  The list gives information about each input
+method, including the string that stands for it in the mode line.
+
+@node Coding Systems, Recognize Coding, Select Input Method, Mule
+@section Coding Systems
+@cindex coding systems
+
+  Users of various languages have established many more-or-less standard
+coding systems for representing them.  XEmacs does not use these coding
+systems internally; instead, it converts from various coding systems to
+its own system when reading data, and converts the internal coding
+system to other coding systems when writing data.  Conversion is
+possible in reading or writing files, in sending or receiving from the
+terminal, and in exchanging data with subprocesses.
+
+  XEmacs assigns a name to each coding system.  Most coding systems are
+used for one language, and the name of the coding system starts with the
+language name.  Some coding systems are used for several languages;
+their names usually start with @samp{iso}.  There are also special
+coding systems @code{binary} and @code{no-conversion} which do not
+convert printing characters at all.
+
+  In addition to converting various representations of non-ASCII
+characters, a coding system can perform end-of-line conversion.  XEmacs
+handles three different conventions for how to separate lines in a file:
+newline, carriage-return linefeed, and just carriage-return.
+
+@table @kbd
+@item C-h C @var{coding} @key{RET}
+Describe coding system @var{coding}.
+
+@item C-h C @key{RET}
+Describe the coding systems currently in use.
+
+@item M-x list-coding-systems
+Display a list of all the supported coding systems.
+@end table
+
+@kindex C-h C
+@findex describe-coding-system
+  The command @kbd{C-h C} (@code{describe-coding-system}) displays
+information about particular coding systems.  You can specify a coding
+system name as argument; alternatively, with an empty argument, it
+describes the coding systems currently selected for various purposes,
+both in the current buffer and as the defaults, and the priority list
+for recognizing coding systems (@pxref{Recognize Coding}).
+
+@findex list-coding-systems
+  To display a list of all the supported coding systems, type @kbd{M-x
+list-coding-systems}.  The list gives information about each coding
+system, including the letter that stands for it in the mode line
+(@pxref{Mode Line}).
+
+  Each of the coding systems that appear in this list---except for
+@code{binary}, which means no conversion of any kind---specifies how and
+whether to convert printing characters, but leaves the choice of
+end-of-line conversion to be decided based on the contents of each file.
+For example, if the file appears to use carriage-return linefeed between
+lines, that end-of-line conversion will be used.
+
+  Each of the listed coding systems has three variants which specify
+exactly what to do for end-of-line conversion:
+
+@table @code
+@item @dots{}-unix
+Don't do any end-of-line conversion; assume the file uses
+newline to separate lines.  (This is the convention normally used
+on Unix and GNU systems.)
+
+@item @dots{}-dos
+Assume the file uses carriage-return linefeed to separate lines,
+and do the appropriate conversion.  (This is the convention normally used
+on Microsoft systems.)
+
+@item @dots{}-mac
+Assume the file uses carriage-return to separate lines, and do the
+appropriate conversion.  (This is the convention normally used on the
+Macintosh system.)
+@end table
+
+  These variant coding systems are omitted from the
+@code{list-coding-systems} display for brevity, since they are entirely
+predictable.  For example, the coding system @code{iso-8859-1} has
+variants @code{iso-8859-1-unix}, @code{iso-8859-1-dos} and
+@code{iso-8859-1-mac}.
+
+  In contrast, the coding system @code{binary} specifies no character
+code conversion at all---none for non-Latin-1 byte values and none for
+end of line.  This is useful for reading or writing binary files, tar
+files, and other files that must be examined verbatim.
+
+  The easiest way to edit a file with no conversion of any kind is with
+the @kbd{M-x find-file-literally} command.  This uses @code{binary}, and
+also suppresses other XEmacs features that might convert the file
+contents before you see them.  @xref{Visiting}.
+
+  The coding system @code{no-conversion} means that the file contains
+non-Latin-1 characters stored with the internal XEmacs encoding.  It
+handles end-of-line conversion based on the data encountered, and has
+the usual three variants to specify the kind of end-of-line conversion.
+
+
+@node Recognize Coding, Specify Coding, Coding Systems, Mule
+@section Recognizing Coding Systems
+
+  Most of the time, XEmacs can recognize which coding system to use for
+any given file--once you have specified your preferences.
+
+  Some coding systems can be recognized or distinguished by which byte
+sequences appear in the data.  However, there are coding systems that
+cannot be distinguished, not even potentially.  For example, there is no
+way to distinguish between Latin-1 and Latin-2; they use the same byte
+values with different meanings.
+
+  XEmacs handles this situation by means of a priority list of coding
+systems.  Whenever XEmacs reads a file, if you do not specify the coding
+system to use, XEmacs checks the data against each coding system,
+starting with the first in priority and working down the list, until it
+finds a coding system that fits the data.  Then it converts the file
+contents assuming that they are represented in this coding system.
+
+  The priority list of coding systems depends on the selected language
+environment (@pxref{Language Environments}).  For example, if you use
+French, you probably want XEmacs to prefer Latin-1 to Latin-2; if you
+use Czech, you probably want Latin-2 to be preferred.  This is one of
+the reasons to specify a language environment.
+
+@findex prefer-coding-system
+  However, you can alter the priority list in detail with the command
+@kbd{M-x prefer-coding-system}.  This command reads the name of a coding
+system from the minibuffer, and adds it to the front of the priority
+list, so that it is preferred to all others.  If you use this command
+several times, each use adds one element to the front of the priority
+list.
+
+@vindex file-coding-system-alist
+  Sometimes a file name indicates which coding system to use for the
+file.  The variable @code{file-coding-system-alist} specifies this
+correspondence.  There is a special function
+@code{modify-coding-system-alist} for adding elements to this list.  For
+example, to read and write all @samp{.txt} using the coding system
+@code{china-iso-8bit}, you can execute this Lisp expression:
+
+@smallexample
+(modify-coding-system-alist 'file "\\.txt\\'" 'china-iso-8bit)
+@end smallexample
+
+@noindent
+The first argument should be @code{file}, the second argument should be
+a regular expression that determines which files this applies to, and
+the third argument says which coding system to use for these files.
+
+@vindex coding
+  You can specify the coding system for a particular file using the
+@samp{-*-@dots{}-*-} construct at the beginning of a file, or a local
+variables list at the end (@pxref{File Variables}).  You do this by
+defining a value for the ``variable'' named @code{coding}.  XEmacs does
+not really have a variable @code{coding}; instead of setting a variable,
+it uses the specified coding system for the file.  For example,
+@samp{-*-mode: C; coding: iso-8859-1;-*-} specifies use of the
+iso-8859-1 coding system, as well as C mode.
+
+@vindex buffer-file-coding-system
+  Once XEmacs has chosen a coding system for a buffer, it stores that
+coding system in @code{buffer-file-coding-system} and uses that coding
+system, by default, for operations that write from this buffer into a
+file.  This includes the commands @code{save-buffer} and
+@code{write-region}.  If you want to write files from this buffer using
+a different coding system, you can specify a different coding system for
+the buffer using @code{set-buffer-file-coding-system} (@pxref{Specify
+Coding}).
+
+
+@node Specify Coding,  , Recognize Coding, Mule
+@section Specifying a Coding System
+
+  In cases where XEmacs does not automatically choose the right coding
+system, you can use these commands to specify one:
+
+@table @kbd
+@item C-x @key{RET} f @var{coding} @key{RET}
+Use coding system @var{coding} for the visited file
+in the current buffer.
+
+@item C-x @key{RET} c @var{coding} @key{RET}
+Specify coding system @var{coding} for the immediately following
+command.
+
+@item C-x @key{RET} k @var{coding} @key{RET}
+Use coding system @var{coding} for keyboard input.
+
+@item C-x @key{RET} t @var{coding} @key{RET}
+Use coding system @var{coding} for terminal output.
+
+@item C-x @key{RET} p @var{coding} @key{RET}
+Use coding system @var{coding} for subprocess input and output
+in the current buffer.
+@end table
+
+@kindex C-x RET f
+@findex set-buffer-file-coding-system
+  The command @kbd{C-x RET f} (@code{set-buffer-file-coding-system})
+specifies the file coding system for the current buffer---in other
+words, which coding system to use when saving or rereading the visited
+file.  You specify which coding system using the minibuffer.  Since this
+command applies to a file you have already visited, it affects only the
+way the file is saved.
+
+@kindex C-x RET c
+@findex universal-coding-system-argument
+  Another way to specify the coding system for a file is when you visit
+the file.  First use the command @kbd{C-x @key{RET} c}
+(@code{universal-coding-system-argument}); this command uses the
+minibuffer to read a coding system name.  After you exit the minibuffer,
+the specified coding system is used for @emph{the immediately following
+command}.
+
+  So if the immediately following command is @kbd{C-x C-f}, for example,
+it reads the file using that coding system (and records the coding
+system for when the file is saved).  Or if the immediately following
+command is @kbd{C-x C-w}, it writes the file using that coding system.
+Other file commands affected by a specified coding system include
+@kbd{C-x C-i} and @kbd{C-x C-v}, as well as the other-window variants of
+@kbd{C-x C-f}.
+
+  In addition, if you run some file input commands with the precedent
+@kbd{C-u}, you can specify coding system to read from minibuffer.  So if
+the immediately following command is @kbd{C-x C-f}, for example, it
+reads the file using that coding system (and records the coding system
+for when the file is saved).  Other file commands affected by a
+specified coding system include @kbd{C-x C-i} and @kbd{C-x C-v}, as well
+as the other-window variants of @kbd{C-x C-f}.
+
+@vindex default-buffer-file-coding-system
+  The variable @code{default-buffer-file-coding-system} specifies the
+choice of coding system to use when you create a new file.  It applies
+when you find a new file, and when you create a buffer and then save it
+in a file.  Selecting a language environment typically sets this
+variable to a good choice of default coding system for that language
+environment.
+
+@kindex C-x RET t
+@findex set-terminal-coding-system
+  The command @kbd{C-x @key{RET} t} (@code{set-terminal-coding-system})
+specifies the coding system for terminal output.  If you specify a
+character code for terminal output, all characters output to the
+terminal are translated into that coding system.
+
+  This feature is useful for certain character-only terminals built to
+support specific languages or character sets---for example, European
+terminals that support one of the ISO Latin character sets.
+
+  By default, output to the terminal is not translated at all.
+
+@kindex C-x RET k
+@findex set-keyboard-coding-system
+  The command @kbd{C-x @key{RET} k} (@code{set-keyboard-coding-system})
+specifies the coding system for keyboard input.  Character-code
+translation of keyboard input is useful for terminals with keys that
+send non-ASCII graphic characters---for example, some terminals designed
+for ISO Latin-1 or subsets of it.
+
+  By default, keyboard input is not translated at all.
+
+  There is a similarity between using a coding system translation for
+keyboard input, and using an input method: both define sequences of
+keyboard input that translate into single characters.  However, input
+methods are designed to be convenient for interactive use by humans, and
+the sequences that are translated are typically sequences of ASCII
+printing characters.  Coding systems typically translate sequences of
+non-graphic characters.
+
+@kindex C-x RET p
+@findex set-buffer-process-coding-system
+  The command @kbd{C-x @key{RET} p} (@code{set-buffer-process-coding-system})
+specifies the coding system for input and output to a subprocess.  This
+command applies to the current buffer; normally, each subprocess has its
+own buffer, and thus you can use this command to specify translation to
+and from a particular subprocess by giving the command in the
+corresponding buffer.
+
+  By default, process input and output are not translated at all.
+
+@vindex file-name-coding-system
+  The variable @code{file-name-coding-system} specifies a coding system
+to use for encoding file names.  If you set the variable to a coding
+system name (as a Lisp symbol or a string), XEmacs encodes file names
+using that coding system for all file operations.  This makes it
+possible to use non-Latin-1 characters in file names---or, at least,
+those non-Latin-1 characters which the specified coding system can
+encode.  By default, this variable is @code{nil}, which implies that you
+cannot use non-Latin-1 characters in file names.